Integrated circuits typically have peripheral or input/output (I/O) circuitry and internal core circuitry. The cores of the integrated circuit perform various processing-specific functions and are desired to operate as fast as possible with minimal power consumption. As a result, power supply voltages that are used to power the core circuitry have been getting smaller with the enhancement of semiconductor processing. The I/O circuitry however functions to provide circuit drive strength to drive or provide signals from the core to external sources at a specified signal power. The I/O circuitry also is frequently required to interface with various interface standards. As different voltages are received at an I/O terminal or pad, the I/O electrical characteristics are varied. For example, the rise and fall signal characteristics vary as well as signal propagation times. The variability of the electrical characteristics results in variable performance. As a result, a circuit must be designed with a large amount of timing tolerance to account for the unpredictable signal and timing changes in response to differing I/O voltages.
Numerous circuits are known for changing the drive capability of buffers or buffer strength of buffers that connect to integrated circuit pins such as an I/O pad. However, the known circuits function to adjust drive strength in response to the amount of impedance connected to an integrated circuit pin or configure a fixed amount of buffer drive strength. Such techniques do not generally respond to operational changes encountered as a result of the size of the voltage range used for the output buffer signals.
Other circuits are known for changing the voltage handling capability of output buffers. For example, in U.S. Pat. No. 5,300,835 a circuit that interfaces between signals at 3.3 volts and 5.0 volts is used wherein a bidirectional buffer performs voltage translation between two distinct voltage levels depending upon the direction of the signal transmission. Such circuits perform voltage translation between two designed fixed voltage values and are limited in operation at other voltages, especially lower voltages than a minimum voltage value.